1. Field of the Invention
The present invention relates to a magnetic sensor.
2. Description of the Prior Art
Generally, the magnetic sensor to which the present invention is directed includes an exciting primary winding wound in one direction around an annular iron core and a secondary winding located, relative to the exited magnetic flux generated by the primary winding, such that the interlinking magnetic flux becomes substantially zero. This kind of magnetic sensor serves as a magnetic azimuth director in a system disclosed for example, in U.S. Pat. No. 3,678,593, issued July 25, 1972 to Baker et al. If a magnetic field is applied in a certain diametric direction of the iron core, across the secondary winding, a secondary higher harmonic voltage (hereinafter referred to as a secondary voltage) is generated which corresponds to the magnitude and the direction of the input axis direction component of the secondary winding of the magnetic flux within the iron core generated by the magnetic field. If a plurality of secondary windings are simultaneously located with different input axes, it is possible to detect the direction of the applied magnetic field, that is the magnetic azimuth, from the secondary voltage appearing on each of the secondary windings.
However, since the magnetic sensor of this kind is overexcited, the non-uniform winding of the primary winding causes a non-uniform excited magnetic flux within the annular iron core. As a result, the intensity of the excited magnetic field, corresponding to the secondary windings, becomes different and this causes a magnetic azimuth error to occur.
Also, it is natural that the angular error between the input axes of the plurality of secondary windings becomes the magnetic azimuth error.
In the prior art magnetic sensor of this kind, the primary winding is wound around the annular iron core over the whole periphery thereof as uniformly as possible. The resulting primary winding is inserted into the bobbin of the secondary winding so that the inner diameter or other diameter of the primary winding is taken as the guide member and the secondary winding is wound around the resulting winding. However, according to this prior art method, it is difficult to wind the primary winding uniformly around the annular iron core over its whole periphery. Further, a significant defect occurs in that the winding around the annular iron core can not provide an accurate outer dimension which can be used as a reference to guide the primary winding into the bobbin of the secondary winding.
Further, in the magnetic sensor of this kind, if the winding distribution in the several secondary windings is not uniform, the directions of the input axes of the secondary windings are displaced from the desired direction with the result that a magnetic azimuth error occurs.
In order to obtain a high magnetic azimuth accuracy, it has been proposed that an area on an annular iron core around which a secondary winding is wound be precisely determined and that the secondary winding be wound as uniformly as possible within this area and then a magnetic sensor having a desired accuracy is selected by inspection and test. However, in this prior art method, there is a serious defect that when a magnetic sensor is found which can not provide the desired accuracy, and if the cause thereof lies in the manner in which the winding is wound, the winding is removed and must be wound again around the annular iron core with great care.